1. Brand name corporation in your community, leading to new businesses propping up
2. Increase land-value in the area, leading to higher city taxes
3. Income, corporate and other taxes associated with the company's project & continuous operation
4. Long-term certainty. Most companies wont build a data center only to scrap the project in 2 years.
5. Economic multiplier. If we assume that each job is tied to $100,000 in income, taxes, benefits, etc and there are 2,300 jobs for 24months, we are looking at $345M-460M in 2 years. Run an economic multiplier and you may be reaching the billion mark
6. Plenty of city,state,federal projects run at a negative or neutral economic value. Having a business such as Google offering to bring business to your hometown will certainly make you listen to them and consider their offer.
It becomes a matter of cost/benefit analysis and ensuring that the community accepting this transaction understands and has the option to complain about it.
I agree that if everyone plays this game, we may reach a point where governments are fully subsidizing every business (there are already plenty of businesses subsidized by governments). It is a matter of finding the right balance.